The news is a major breakthrough in the unprecedented two-week struggle to find out what happened to Flight 370, which disappeared shortly after takeoff from Kuala Lumpur to Beijing with 239 passengers and crew aboard on March 8.

Dressed in a black suit, Najib announced the news "with deep sadness and regret" in a brief news conference late Monday night.

He said Malaysia Airlines has informed the families of passengers of the plane's fate.

Najib said the information was based on an unprecedented analysis of satellite data from Inmarsat.

Today, ships are headed to an area of the southern Indian Ocean where floating objects were spotted. They include a vessel that has equipment to detect the plane's black box.

The announcement came the same day as Australian officials said they had spotted two objects in the southern Indian Ocean that could be related to the flight, which has been missing since March 8 with 239 people aboard.

One object is "a grey or green circular object," and the other is "an orange rectangular object," the Australian Maritime Safety Authority said.

The objects are the latest in a series of sightings, including "suspicious objects" reported earlier Monday by a Chinese military plane that was involved in search efforts in the same region, authorities said.

So far, nothing has been definitively linked to Flight 370.

Text message sent to the families of flight MH370 from Malaysian Airlines

Malaysia Airlines sent a text message to Flight 370 before relatives were briefed at hotels according to airline spokeswoman Adlina Azharuddin.

The text message read: "Malaysia Airlines deeply regrets that we have to assume beyond any reasonable doubt that MH370 has been lost and that none of those on board survived. As you will hear in the next hour from Malaysia's Prime Minster we must now accept all evidence suggests the plane went down in the Southern Indian Ocean."

Malaysia Airlines is "working on an arrangement" to fly families of Flight 370 passengers to Australia once wreckage is found, an airline representative said Monday.

Flight 370 passenger's relative: 'All lives are lost' (CNN)

The announcement came the same day as Australian officials said they had spotted two objects in the southern Indian Ocean that could be related to the flight, which has been missing since March 8 with 239 people aboard.

One object is "a grey or green circular object," and the other is "an orange rectangular object," the Australian Maritime Safety Authority said.

The objects are the latest in a series of sightings, including "suspicious objects" reported earlier Monday by a Chinese military plane that was involved in search efforts in the same region, authorities said.